The present invention relates generally to battery chargers, and more particularly, to a polyphase boost inductor battery charger having a switching current spike limiter.
Polyphase boost inductor battery chargers are known in the battery charger art, as illustrated, for example, by the U.S. Pat. No. 5,099,186, assigned to General Motors Corporation, and incorporated herein by reference. As indicated in the above-referenced U.S. Pat. No. 5,099,186, such chargers include a voltage source coupled to the battery to be charged through two or more inductors and a polyphase transistor bridge. The transistors of the bridge are modulated on and off to build up current in the respective inductors, the current being circulated through the free-wheeling diodes of the bridge when the inductor voltage exceeds the battery voltage. In the U.S. Pat. No. 5,099,186, the charger is for the batteries of an electric vehicle, and the inductors are the windings of the vehicle's propulsion motor.
As indicated in the above-referenced U.S. Pat. No. 5,099,186, boost inductor battery chargers work well so long as the peak input voltage does not exceed the battery voltage. If the peak input voltage exceeds the battery voltage, a large, uncontrolled current would flow to the battery through the free-wheeling diodes of the bridge. This situation is obviously undesirable, and limits the utility of this type of battery charger.
While it is known to limit current using a resistor or a transistor operated in the linear region, such devices dissipate power, and therefore require large devices and expensive heat sinks. Typically, the charging current is limited to relatively low levels to control the heat dissipation.
Therefore, it is an objective of the present invention to provide for an improved polyphase boost inductor battery charger having a switching current spike limiter that overcomes the limitations of conventional chargers.